The present invention relates to a method of switching a speech path in a radiotelephone system in which even when a portable-type cordless telephone set is moved through a plurality of service zones, a telephone speech can be achieved with a satisfactory speech quality, and in particular, to a speech path switching method suitable for a private branch radio exchange system.
In the radiotelephone system, as a method of controlling a switching operation between speech paths during a speech, there has been well known, for example, a hand-over control of an automobile telephone. An example of a switch method associated with the hand-over control has been described in pages 197 to 200 of the "Channel Switch During Speech" published on Feb. 10, 1985 (Automobile Telephone, the Electronics and Communication Engineers of Japan). As described in this article, the speech path is automatically switched during a speech; moreover, the switch operation is initiated on the side of a radio channel control station, namely, on a telephone exchange side.
In other words, in an identical radio channel control station, the channel switch is achieved during a speed such that while radio waves of the respective base stations are changed in the proximity of boundaries between service zones, the system selects from a plurality of zones a zone associated with a highest reception level to establish a connection to the zone.
However, in accordance with the conventional technology above, a speech path once established between a radio mobile telephone set (station) and a radio base station equipment may be re-established depending on a result of an operation to monitor a reception level in the radio base station equipment. Consequently, the speech path cannot be re-established on the side of the radio mobile telephone set. Actually, in a speech using radio waves, depending on a combination of a radio mobile telephone set and a radio base station equipment, a speech may be conducted through a speech path in which the radio communication is not carried out in a satisfactory state. Even in such a case, the speech path cannot be re-established from the side of the radio mobile equipment.